Conventional contact lenses are hard lenses polymerized using the principal co-monomer, methyl methacrylate.
Nearly all of these hard contact lenses are manufactured from lens blanks which are tinted or colored. Hard contact lenses are also known in the field as corneal lenses. Most commonly, hard contact lenses are fitted with a diameter which is less than the diameter of the cornea of the eye. This allows for the entire contact lens to be colored and appear quite natural on the eye.
On Oct. 20, 1978, the Contact Lens Manufacturers Association held a convention in which one of its speakers was the president of Glass-Flex Corporation. During this discussion the speaker mentioned the problems involved in coloring entire hard lenses through the use of pigments which presented problems in their ability to disperse uniformly throughout the lens.
Soft contact lenses in contrast to hard lenses are most commonly fitted with a diameter larger than that of the cornea.
Attempts have been made to tint soft contact lenses. One prior art method is to paint or print a colored central portion onto a soft contact lens using an implement such as a brush. This painting or chemical printing process has been practiced by foreign lens makers for several years. Woehlk-Contact-Lenses, Ltd. for Titmus-Eurocon have been producing printed or painted iris soft contact lenses. The clear lens is first fitted to be sure the lens is correct for the patient and then returned to the laboratory for printing..sup.1 FNT 1. Contact Lens Forum, Vol. 3, No. 8, August, 1978, p. 89.
Dr. Leroy G. Meshel, a California ophthalmologist, working with a chemist, Vernon Gregory, has developed a chemical printing process for coloring soft contact lenses. This process, which appears to be quite similar to those mentioned above, colors the surface of the lens after the clear lens has been first fitted by the patient's doctor..sup.2 FNT 2. Contact Lens Forum, Vol. 3, No. 3, March, 1978, pp. 13-17.
There are several problems with the printing type of technique. First, the color is only printed on the lens after it has been manufactured and, therefore, is not uniformly dispersed through the lens material itself. Dr. Meshel admits that the color does tend to fade after several autoclavings and recommends cold chemical sterilization..sup.3 Secondly, the clear lens must be first manufactured and fit on the patient's eye before the coloring takes place. This requires the lenses to be sent back to the manufacturing company by the patient's doctor. Thirdly, the printing process requires additional fabrication steps and equipment. FNT 3. Ibid., p. 16.
Water soluble dyes have also been used to provide the tinting..sup.4 Newcomer and Janoff selected dyes on the basis of their wate solubility and previous F.D.A. approval for human use or for their commercial availability as biological dyes. The results of this work were that the water soluble dyes tend to leach, especially with repeated thermal aspeticizing cycles which could permanently stain the cornea. The authors also noted that the large diameter of the Soflens.RTM. would cause the margin of a tinted lens to be very conspicuous against the white sclera of the eye and that this might produce an objectionable cosmetic effect for the wearer. In addition, water soluble dyes in long term contact with the eye might permantly stain the ocular tissue. FNT 4. Newcomer, P. C. and Janoff, L. E., American Journal of Optometry and Physiological Optics, 54 (3) 160-164 (1977), "Methods of Tinting Soflens.RTM. Contact Lenses."
Due to the large size of soft contact lenses, if the lens is of one color, the appearance on the eye is very unnatural. Therefore, a natural appearing soft contact lens should have a colored central area and a clear outer area so that the colored portion will not cover the sclera of the eye. Such a configuration, while very desirable, causes severe fabrication problems. The colors must not bleed or leach from one area of the lens to another, nor must they leach into the tear fluid and thereby ultimately into the eye. The colored area and the clear area must normally be concentric and be easily aligned in the fabrication step.
Ideally, the coloring compound dye should be stable in color and intensity and maintain a good tone, i.e., not cloudy or hazy after the lens is hydrated. In addition, it must not leach.
The more common water soluble dyes such as methylene blue chloride when used for this purpose will equilibrate on hydration to a point at which the lens is one solid color over its entire surface area.
The difficulties described above may be avoided by using water insoluble dyes or dyes which are so structured that they may be polymer bound to the backbone of the polymerized co-monomer mixture. In either case, a lens blank configuration is disclosed which allows for both clear and colored portions to be fabricated in the resulting contact lens.
The contact lens of the present invention, therefore, possesses the following properties and advantages:
1. A contact lens which appears completely natural as worn on the eye by having a colored portion which does not cover any of the sclera of the eye. PA1 2. A colored lens which is completely safe for the wearer possessing a color which will not bleed or leach from the lens into the eye or from one part of the lens to another. PA1 3. A contact lens which offers outstanding aesthetic beauty to the eye of the wearer as well as covering unattractive irregularities in the eye. PA1 4. A colored contact lens which will retain its color despite aging or nightly sterilization, i.e., boiling. PA1 5. A colored contact lens that can be completely fabricated before fitting the patient's eye. PA1 6. A colored contact lens that can be fabricated by incorporating the teachings of the present invention with conventional lens manufacturing techniques thereby eliminating the need for additional equipment and processes.